Fixes: #130674 

Before: The dropdown menu was not closed if empty text was provided

After: The dropdown menu is closed even if empty text is provided

https://github.com/flutter/flutter/assets/61322712/fccac501-9fca-4f60-8a94-abfc50552ec9

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*